Screen &1 for program &2 does not exist

What causes this issue?

You have assigned a screen number &v1& to the function module &v3&.
This screen must be created for the main program &v2& of the function
module. This is, however, not the case.

System Response

The system issues an error message and will not allow you to continue with this transaction until the error is resolved.

How to fix this error?

Choose an existing screen number.

Error message extract from SAP system. Copyright SAP SE.